The present invention relates to a coated cutting tool comprising one or more metallic interlayers in-between two non-metallic, functional layers or layer systems. The cutting tools according to the present invention will exhibit superior life time due to an increased toughness, thus showing better ability to withstand changes in load. In addition, this invention facilitates deposition of thicker PVD-coatings without the risk of spalling along the edge line, hence thicker coatings with better flank wear resistance can be deposited. The tougher behavior of the coatings facilitates reasonably thick coatings even on sharp or ground edges.
In general, the life time of a cutting tool is significantly prolonged if a coating is deposited onto its surface. Most cutting tools today are coated with PVD or CVD coatings like Ti(C,N), TiN, (Ti,Al)N, (Ti,Si)N, (Al,Cr)N or Al2O3. PVD coatings have several attractive properties compared to CVD coatings, for instance, finer grained coatings and compressive stresses in the as-deposited state, which gives a better ability to tolerate changes in load. However, PVD coatings usually have to be quite thin, since thicker PVD coatings may cause spalling, frittering, so-called edge-line spalling and flaking, either spontaneously, usually around the edge line, or during machining.
The maximum coating thickness that can be deposited on a tool before spalling occurs depend on the edge radius, ER. Sharp edges with small ER, and ground edges are particularly prone to spalling and flaking along the edge line, and thus thin coatings are usually deposited. However, slightly thicker coatings would be preferred if the edge line could be kept intact since thicker coatings in most cases would lead to an increased tool life due to better wear resistance.
Deposition of metallic layers with PVD techniques is an established technology in PVD-processes. It is well-known that depositing a metallic layer directly onto the surface of the substrate before depositing the rest of the coating can enhance the adhesion of the coating.
A few attempts have also been made to deposit metallic layers between non-metallic layers.
US2002/0102400 A describes a wear resistant coating comprising alternating metallic and ceramic layers. The coating will have a fine grained surface with low micro-roughness. The coating is preferably deposited onto substrates of steel, titanium, or carbide e.g. TiC, but preferably steel. The substrates are preferably in the form of a dental tool, surgical tool or cutting tool. In the examples, dental scalers of steel are provided with the coating.